I think reputation should be the scarce resource for preventing sybil attacks, and not computing power via proof-of-work. The latter won't even work with new (and therefore small) blockchain networks, since a 51% attack is trivial. Reputation replaces distributed consensus with probabilistic value, relative to each participant. That's actually how currencies are discounted when being converted. Wildcat money during the free banking era was heavily discounted. Currencies and debts are accepted locally and from trusted people.